Testing of output drivers of integrated circuit is known. The known testing methods use external dedicated test equipment which individually tests each output port present on the integrated circuit. However, such testing is time consuming and requires expensive equipment.
Furthermore, a die is typically packaged e.g. using wirebonds, and mounted on a board. Its output ports are connected to external devices via transmission lines, formed by signal traces on a package and a printed circuit board. However, the presence of transmission lines connected to the output ports results in loss of the signal integrity due to inaccurate impedance matching. Thus for the sake of proper impedance matching between the integrated circuit output driver and conjugated transmission line the knowing of ration between the mentioned driver and the transmission line impedances is required.
United States Patent Application US2006/0020412 discloses a system to which a data signal which represents a known binary series is presented. The system includes a comparator which compares the data signal with a threshold level and outputs a high voltage or a low voltage depending on whether the level of the data signal is above or below the threshold level. A binary sampler samples the output signal from the comparator. The sampled signal is compared by an error compare circuit to determine whether the sample signal differs from the value defined by the known binary series. The amount of errors determined by the error compare circuit is counted by an error counter and the ratio of error counts verses the number of sample cycles defines the bit error rate (BER). By observing the variation in the BER as a function of threshold level and sampling phase, analog characteristics of the data signal are determined, such as the time when the data signal transitions from binary zero to a binary one.
However, this prior art system only allows a quality estimation of the communication channel (good or bad) based on BER measurements, without real impedance measurement.